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Fast and selective determination of total protein in milk powder via titration of moving reaction boundary electrophoresis

Authors

  • Cheng-ye Guo,

    1. Laboratory of Bioseparation and Analytical Biochemistry, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
    2. School of Environment and Chemistry, Shanghai Normal University, Shanghai, China
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    • These authors have contributed equally to this study.

  • Hou-yu Wang,

    1. Laboratory of Bioseparation and Analytical Biochemistry, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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    • These authors have contributed equally to this study.

  • Xiao-Ping Liu,

    1. Laboratory of Bioseparation and Analytical Biochemistry, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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  • Liu-yin Fan,

    1. Laboratory of Bioseparation and Analytical Biochemistry, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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  • Lei Zhang,

    1. School of Environment and Chemistry, Shanghai Normal University, Shanghai, China
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  • Cheng-xi Cao

    Corresponding author
    • Laboratory of Bioseparation and Analytical Biochemistry, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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  • Colour Online: See the article online to view Figs. 1, 2, 4‒6 and 8 in colour.

Correspondence: Professor Cheng-Xi Cao, School of Life Science and Biotechnology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China

E-mail: cxcao@sjtu.edu.cn

Fax: +86-21-3420 5820

Abstract

In this paper, moving reaction boundary titration (MRBT) was developed for rapid and accurate quantification of total protein in infant milk powder, from the concept of moving reaction boundary (MRB) electrophoresis. In the method, the MRB was formed by the hydroxide ions and the acidic residues of milk proteins immobilized via cross-linked polyacrylamide gel (PAG), an acid-base indicator was used to denote the boundary motion. As a proof of concept, we chose five brands of infant milk powders to study the feasibility of MRBT method. The calibration curve of MRB velocity versus logarithmic total protein content of infant milk powder sample was established based on the visual signal of MRB motion as a function of logarithmic milk protein content. Weak influence of nonprotein nitrogen (NPN) reagents (e.g., melamine and urea) on MRBT method was observed, due to the fact that MRB was formed with hydroxide ions and the acidic residues of captured milk proteins, rather than the alkaline residues or the NPN reagents added. The total protein contents in infant milk powder samples detected via the MRBT method were in good agreement with those achieved by the classic Kjeldahl method. In addition, the developed method had much faster measuring speed compared with the Kjeldahl method.

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